A Comparison of Methods for Assessing the Antioxidant Expression in Posidonia oceanica (L.) Delile

Non-enzymatic antioxidants, such as polyphenols, can counteract free radicals and other potentially toxic oxidants produced by marine plants exposed to stress. In this study, we assessed different methods for measuring antioxidant capacities and condensed tannins in the seagrass Posidonia oceanica (L.) Delile. Two polyphenol extraction methods, direct and sequential, were compared to determine their efficiencies. Condensed tannins were assayed directly on leaf flour using a modified HCl-butanol-acetone-iron reagent method. Total antioxidant capacities were assayed with the ABTS, CUPRAC, and ORAC methods, both on extracts and on powdered samples (QUENCHER). The direct assays showed higher sensitivity compared to their in-solution counterparts. Our results indicate that in-depth measurement of antioxidant compounds and capacities can be achieved by direct assays on P. oceanica powder samples, and these data can be used to assess changes in the plant biochemistry due to the exposure to varying biotic and abiotic conditions.